Elizabeth Anscombe and Anthony Kenny disagree on whether or not it is possible to doubt the existence of one’s own body. Anscombe believes that such doubt makes sense while Kenny argues that it could make sense only if one supposed that he had become a bodyless Cartesian ego. To resolve the issue I explore the knowledge one acquires of himself, and thus the manner in which such knowledge might be weakened into doubt. Siding with Anscombe, I argue that under the conditions of sensory deprivation some very basic questions asked of oneself such as, “Which body?” cannot be answered. Without such answers, one can be uncertain about his own body. Such uncertainty, however, is to be explained by the autonomy of the relevant ‘J-thoughts’ and not because one had become a Cartesian ego